This invention relates generally to electrodynamic machines and more particularly to such a machine for powering an electric motorized wheel on an off-highway truck of the type used to haul heavy payloads in open pit mines.
Motorized wheels are useful on large off-highway traction vehicles for propelling or retarding the vehicle in an energy efficient manner. In such a wheel the magnet frame or stator of a cylindrical electric traction motor serves as a non-rotating axle for the wheel. The stator is suitably affixed to the frame or body of the vehicle, and it rotatably supports the wheel hub on which is mounted at least one large pneumatic tire. Transmission of power is accomplished by a speed-reducing gear train and a torque tube connected between the rotor of the motor and the coaxial hub of the wheel. A mechanism of this type is shown and described in U.S. Pat. No. 2,899,005--Speicher. In such a wheel, the gear train, which typically comprises a sun pinion and three planet gears, is housed in a gear case on the inboard side of the wheel (i.e., the side next to the body of the vehicle). In the motor, which is usually a direct current (d-c) type, a commutator and associated brushes are used to supply electric current to armature windings on the rotor, and since these parts require periodic inspection and maintenance, the commutator and brushes are located so as to be accessible from the outboard side of the wheel.
In the Speicher wheel, the rotor of the motor can be readily removed from the outboard side for servicing or replacement, as needed. However, it is more difficult to service the pole pieces, field coils, and brush holders of the motor because they are attached to the stator which cannot be removed in the Speicher wheel without first removing the whole wheel from the vehicle and disassembling the pneumatic tire and other major components. For more convenient servicability, it is desirable to construct a motorized wheel so that the motor stator and all of the parts assembled therewith are removable as a unit without disassembling the hub of the wheel from the vehicle.
In another prior art motorized wheel, the motor plugs into a cylindrical member or barrel which in turn rotatably supports the hub of the wheel, whereby the whole stator assembly of the motor can be removed from the outboard side of the wheel. With the stator assembly locked in place inside the barrel, there is a tight interference fit between its outside circumference and the cooperating inside surface of the barrel. Whenever the motor is removed from the wheel and the wheel is not removed from the vehicle, the barrel alone carries the wheel's proportionate share of the vehicle's weight. The referenced arrangement is disadvantageous because of the possibility that the stator will become stuck inside the barrel due to fretting or corrosion. Furthermore, the removable stator is not utilized for the dual purposes of both providing the magnet frame of the motor and supporting the weight of the vehicle. Consequently the additional barrel of this prior art motorized wheel contributes undesirably to the size and manufacturing cost of the wheel and to the non-payload weight of the vehicle.